BIOLOGY - A SCIENCE OF EXCEPTION -
Some common examples to prove it are -
1. Embryos of dicot plants have 2 cotyledons but in cuscuta (Dodder plant or amer bel or Akash bel) cotyledons are absent.
2. Nucleus generally present in all cells except R.B.C. of mammals (in camel & lama present), sieve tubes of phloem of plants.
3. DNA present in all animal viruses except influenza virus, polio virus, reo virus in which RNA present.
4. RNA present in all plant viruses except cauliflower mosaic virus in which DNA present.
5. In human 206 bones present, in human having 6 fingers in one hand 209 bones present.
6. In birds urinnary bladder absent but present in ostrich.
7. Kangaroo rat never drinks water in life.
8. DNA is double strandded but in fx 174 bacteriophage single stranded DNA present.
9. RNA is single strended but in wound tumour virus & reo virus it is double stranded.
10. Sexual reproduction usually occurs at puberty but in Ambyostoma's axolotal larva, it occurs at larval stage. This process is paedeogenesis and stage is neotany.
11. Blood of all vertebrtes is red but in corcharinus (shark) it is colour less.
12. Mammals are viviparous while Platypus, Echidna are oviparous & Kangroos or marsupials (having marsupium ponch) are ovo-viviparous.
13. Fishes usually respire by gills but in Protopterus, Lepidosiren, Ceratodus lungs present (Dipnoi).
14. Heart of all reptiles is incomplete 4 chambered but in crocodelia 4 chambered.
15. In pisces heart is 2 chambered but in dipnoi 3 chambered.
16. Mostly birds fly except ostrich, kiwi & penguine.
17. Mammals do not fly except bat & lemur.
18. Usually young ones are produced from zygotes while dron (male) of honey bee are formed from unfertilized egg by parthenogenesis. Dron is not having father but forefather (Nana) is present.
19. Chromosomes number in diseased human may be 45 or 47.
20. Femur is largest bone of human body while stapes is smallest bone.